Regeneration of ion exchangers



Feb. 10; 1953 B. A. SARD 2,628,191

REGENERATION OF ION EXCHANGERS Filed Feb. 18, 1948 2 SIIEETSSHEET 1 ACID/TY Y TIME I6 29 Z2 2/ l l 2 ll will: 55

INVENTOR BERN/1R0 ABEL 5M0 ATTORNEY Feb. 10, 1953 B. A. SARD 2,528,191

REGENERATION OF ION EXCHANGERS Filed Feb. 18, 1948 2 SHEET$SHEET 2 HLHLL SEQUEA/[E TIME)? 1 l NVENTO R BERNARD 45a .S'A/?0 ATTORNEY Patented Feb. 10, 1953 REGENERATION 0F ION EXCHANGERS Bernard Abel Sard, Osterley, England, assignor to The Permutit Company, New York, N. Y., a corporation of Delaware Application February 18, 1948, Serial No. 9,302 In Great Britain October 29, 1946 Section 1, Public Law 690, August 8, 1946 Patent expires October 29, 1966 11 Claims.

This invention relates to the regeneration of a bed of cation exchange material used for the treatment of liquids containing dissolved cations. More particularly, the invention is concerned with a process and apparatus for determining when a bed of cation exchange material charged with exchangeable hydrogen ions becomes exhausted in its normal operation so that regeneration is required.

The treatment of liquids containing cations, such as Water containing sodium, calcium, magnesium and similar cations, with a cation exchange material known as a hydrogen ion exchanger, has been used for some time. The exchange materials used in this so-called hydrogen cycle are organic materials, granular in form, which are regenerated from time to time, as may be necessary, with an acid solution. After regeneration with the acid, the cation exchange material removes sodium, calcium and magnesium ions from water passed through a bed of the material, giving up hydrogen ions to the water in place of the metallic cations removed. Eventually, however, the cation exchange material becomes exhausted, and at this point it has to be regenerated again. During the regenera tion stage, the acid is introduced into the bed of material for regeneration, then washed out, and the flow of water to be treated through the bed is again started.

It is dificult, however, to determine with exactness the point during the working part of the cycle when the exchange material becomes sufficiently exhausted to require regeneration with the acid. Two main methods used heretofore for this purpose involve either periodic chemical testing of the eflluent from the bed of exchange material, or the passage of a predetermined quantity of the water or other liquid undergoing treatment. Neither one of these methods is completely satisfactory. If chemical testing of the efiluent is used, it is necessary to make successive determinations of the acidity of the efiluent and determine the point of the working stage at which a rapid fall of acidity from the normal value occurs. This method is not only somewhat cumbersome for practical operation, but also may give confusing results because the acidity of the effluent is dependent, to some extent at least, upon the cation content of the raw water or other liquid undergoing treatment. Thus, a fall in the acidity of the effiuent may indicate exhaustion of the cation exchange material, or it may simply indicate a variation in the cation content of the raw liquid introduced into the cation exchange material.

dissolved 1 The method of regeneration based upon passage of a predetermined quantity of liquid undergoing treatment is likewise not entirely satisfactory, because in this case an adequate safety factor or margin must be allowed to take care of any variation in the cation content of the raw liquid entering the exchanger. Consequently, this method frequently results in the incomplete use of the full exchange capacity of the cation exchange material and, therefore, more frequent regeneration using more regenerating acid than is necessary.

One object of this invention is to provide a process and apparatus by which these disadvantages can be overcome and the end point of the working stage determined simply and accurately, regardless of fluctuations in the cation content of the raw liquid undergoing treatment.

A further object of this invention is to determine the end point of the working stage of such a cation exchange material by comparing the electrical conductivity of the efiluent from the bed of exchange material with the electrical conductivity of a portion of the efiluent that has been passed through a diiierent quantity of the exchange material.

The invention will be better understood by reference to the accompanying drawings, in which Figure 1 is a graph of the acidity of the eiiluent plotted against time during the working stage of a hydrogen ion exchange material used to treat water of constant cation content at a steady rate.

Figure 2 is a schematic illustration of a hydrogen ion exchange unit equipped to determine the end point of the working stage in accordance with my invention.

Figure 3 is a schematic illustration of a hydrogen ion exchange unit equipped to determine the end point of the working stage and initiate auto matically the regeneration of the ion exchange material.

If, after a bed of cation exchange material is regenerated acid, water of constant composition is passed through the bed at a steady rate and the acidity of the effiuent is plotted against time, a curve of the form shown in Figure l is obtained. As the Water is first passed through the bed the efliuent has a rather high acidity, as indicated at the point X, and drops rather sharply to the point Y as some free acid left in the bed is gradually washed out. The acidity then changes only very slowly during the operation of the exchanger as shown by the curve between the points Y and Z, and is dependent upon the original cation content associated with the anions of strong acids in the raw water undergoing treatment. At the point Z, however, the cation exchange material becomes exhausted, for practical purposes, and if the fiow of water is continued, the acidity of the efiluent thereafter falls rapidly until it becomes zero. In fact, if the raw water undergoing treatment is alkaline, alkalinity will appear in the efiluent and gradually increase until it reaches the same value as that of the raw liquid entering the cation exchanger.

In accordance with my invention, the point Z on this curve is determined readily and simply by comparing the electrical conductivity of the efiluent from the exchange unit with the electrical conductivity of a sample of the eilluent subjected to a difierent quantity of hydrogen ion exchange material. This portion of the eilluent used for comparison may be a portion of the eliluent from the unit passed through an auxiliary hydrogen ion exchanger. A comparison is thus provided between two samples of treated water containing at the exhaustion point difierent quantities of hydrogen ions and, therefore, different quantities of metallic cations. Since the equivalent conductance of hydrogen ions is much greater than the equivalent conductance of metallic cations, these two samples, at this stage, would have substantially different electrical conductivities or resistances, even though the sum of the hydrogen and metallic cations in the samples is not changed. Before the point Z is reached on the curve in Figure 1, both samples will contain approximately the same quantity of hydrogen ions and therefore have approximately the same electrical conductivity.

Such a procedure may be employed in a plant employing single cation exchange units, or in a plant in which two or more containers are filled with cation exchange material and connected either in series or in parallel.

When an auxiliary cation exchanger is employed, it is used only for test purposes and therefore may be made of relatively small size and receive only a small part of the efiiuent from the main cation exchange unit. The effiuent from this auxiliary unit may be mixed with the main eiiluent from the main exchange unit as it goes to storage or service, or it may be run to waste.

One suitable arrangement for operation in accordance with my invention is shown in Figure 2, in which a container or tank is provided with a bed of suitable depth of organic cation exchange material. This tank is provided with pipes l l and I2 for the introduction or withdrawal of liquid, and pipes II and i2 are connected together outside the tank by the pipe l3 which in turn is connected to the inlet [4 for the raw water to be treated. Valves I5 and It in the pipe 13 permit raw water from the inlet [4 to be introduced either into the lower part of the tank for backwashing, or into the upper part of the tank for the ion exchange treatment. Pipe II is preferably provided with an extension I? having a suitable valve l8 through which liquid can be run to waste. The lower end of pipe l3 may likewise be provided with an extension 19 and a suitable valve 20 through which residual free acid and wash water may be run to waste.

The water which has been treated passes through the pipe 2| controlled by valve 22 and thence to service or storage, as may be desired. The tank It is also provided with an inlet-22a for the regenerating acid from tank 23, the introduction of which is controlled by the valve 24 and distributed over the cation exchange material inside the tank by a baffle plate or difiuser 25.

In accordance with my invention, the normal efiiuent passing to service through the outlet 2| passes through a chamber 26 fitted with a pair of electrodes 21. Also, a portion of the effluent is by-passed from the main outlet through the pipe 28 under control of valve 29 through a small auxiliary hydrogen ion exchanger 30 and thence through a chamber 3| between the electrodes 32 and either run to waste or combined with the effluent from the outlet 2|.

The pairs of electrodes 2! and 32 with the liquid flowing between them constitute variable resistances which are connected electrically in series with each other and with a source of potential, such as a battery 33, by the wires 34, 35 and 3B. A pair of fixed resistances 3'! and 38 are connected in series with each other across the battery 33, and a galvanometer or other similar instrument 39 is connected across the system between the resistances 37 and 38 and the electrodes 21 and 32, thus providing a Wheatstone bridge.

In the operation of this device, the exchange material in the tank I 0 and in the auxiliary exchange unit 30, after being regenerated with acid, is used to remove metallic cations from water. The normal effluent from this tank, which has virtually all of its metallic cations removed and contains hydrogen ions in place thereof, passes between the electrode 21 and creates a resistance at this point of a given value. A portion of this eflluent is withdrawn through the pipe 28 and passed through the exchanger 30 which does not alter the chemical composition of the water substantially at this stage, so that the efiiuent from the auxiliary exchanger 30 when passed between the electrodes 32 creates a resistance approximately equal to the resistance between the electrodes 21. Thus, if the resistances 3'! and 38 are also balanced with respect to each other, the needle of the galvanometer 39 will not be deflected in either direction.

This condition will be maintained regardless of normal fluctuations in metallic cation content of the raw water undergoing treatment because the two efiiuents from the tank It] and the auxiliary exchanger 30 will have substan tially the same resistance as each other as long as the exchange material in the tank It is performing its proper function. However, as soon as the efiluent from the tank l0 begins to contain quantities of metallic cations which have not been converted to hydrogen ions, the resistance between the electrodes 21 will become somewhat lower and a sample of this Water passed through the auxiliary exchanger 30 will then contain a higher hydrogen ion content with consequent less resistance between the electrodes 32. As this occurs, the needle of the galvanometer 39 will swing over from the neutral position indicating that the exchange material in the tank In needs regeneration.

At this stage, the flow of raw water to the unit is shut off by closing the valves 15, 22 and 29, and the valves I 8 and I6 are opened to backwash the exchange material in the tank I 0. When the material has been backwashed and loosened sufficiently, the valves 18 and I 6 are closed, and acid is introduced into the tank 10 by opening the valve 24. Normally this acid would be run to waste by simply opening the valve 26, but in this case it may be desirable to use some of the waste acid to regenerate the exchange material in the auxiliary exchanger 30. Consequently, the valve 29 is opened to pass part of the acid through the exchanger 30 and the material in both exchange units is then washed by opening the valve i5. Valve 20 may be opened sufficiently to run to Waste the acid and wash water that is not needed for passage through the exchanger 30. After suflicient washing has taken place, the valve 20 is closed, and the valves 22 and 29 are opened to start the next Working stage.

It is also possible, as will be apparent to those skilled in the art, to utilize this process and apparatus for performing the regeneration of the unit automatically. In the arrangement shown in Figure 3, the reference numerals applied indicate the same parts as those indicated and described in connection with Figure 2. The apparatus is essentially the same except that all of the valves are operated by either motors or solenoids, and the galvanometer is of the limit contact type, so that when the needle of the ordinary galvanometer would be deflected a certain distance, the contacts of the galvanometer 4d are closed completing a circuit to the coil of the solenoid M, which in turn closes the switch 42 and starts the motor 43 driving the sequence timer 44. The sequence timer 44 supplies power through the pairs of conductors 45 to the various valves described in connection with Figure 2 in the proper sequence to perform the operations of backwashing, regeneration with acid, washing and restoring the working stage automatically.

It will also be apparent that while Figure 3 indicates one type of automatic regeneration, the same principle may readily be employed to initiate automatic regeneration performed by a single motor driven multi-port valve or by various other means, as will be readily understood by those skilled in the art.

A Wheatstone bridge has been described as one method and means for comparing the resistance or the conductivity of the eflluent from the main exchange unit in with the efiluent from the auxiliary exchange unit 30. However, any other suitable electrical instruments or system may be used either to measure or compare the electrical conductivities or resistances of the two samples of eiiluent.

Also, it will be apparent that if two hydrogen ion exchangers are connected to operate in series, the efiluent from the second exchanger in the series may be used for the comparison instead of the efliuent from a separate auxiliary exchanger.

The terms and expressions which I have employed are used as terms of description and not of limitation, and I have no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

I claim:

1. A process of determining when to regenerate a hydrogen ion exchanger which comprises bypassing a portion of the effluent from the exchanger through a small auxiliary hydrogen ion exchanger, measuring the conductivities of the effluents from said exchangers, and regenerating said first exchanger when said conductivities become substantially difierent from each other.

2. Apparatus for determining when to regenerate a hydrogen ion exchanger which comprises means for measuring the electrical conductivities of the effluent from the exchanger and of a sample of said eifiuent which has been passed through a different quantity of the hydrogen ion exchange material, and means for indicating when' these conductivities become substantially different from each other.

3. Apparatus for determining when to regencrate a hydrogen ion exchanger which comprises means for measuring the electrical conductivities of the efiluent from the exchanger and of a sample of said effluent which has been passed through a difierent quantity of the hydrogen ion exchange material, and means for initiating regeneration of the exchanger when the conductivities become substantially dil ferent from each other.

4. Apparatus for determining when to regenerate a hydrogen ion exchanger which comprises means for measuring the electrical conductivities of the efliuent from the exchanger and of a sample of the same efiluent which has been passed through an additional quantity of fully regenerated hydrogen ion exchange material, and means for indicating when these conductivities become substantially different from each other.

5. Apparatus for determining when to regenerate a hyrogen ion exchanger which comprises .eans for measuring the electrical conductivities of the efiluent from the exchanger and of a sample of the same eliluent which has been passed through an additional quantity of fully regenerated hydrogen ion exchange material, and means for initiating regeneration of the exchanger when the conductivities become substantially different from each other.

6. In combination with a hydrogen ion exchanger, two pairs of electrodes connected to form balancing resistors in a Wheatstone bridge, means for passing the efiluent from the exchanger between one pair of electrodes, and means for passing between the other pair of electrodes a sample of the same efiiuent which has been subjected to the action of a difierent quantity of the hydrogen ion exchange material.

'7. In combination with a hydrogen ion exchanger, two pairs of electrodes connected to form balancing resistors in a Wheatstone bridge, means for passing the eiiluent from the exchanger between one pair of electrodes, and means for passing between the other pair of electrodes a sample of said eiiluent after it has been passed through an additonal quantity of fully regenerated hydrogen ion exchange material.

8. In combination with a hydrogen ion exchanger, two pairs of electrodes connected to form balancing resistors in a Wheatstone bridge, means for passing the effluent from the exchanger between one pair of electrodes, means for passing between the other pair of electrodes a sample of said efiiuent which has been subjected to the action of a different quantity of the hydrogen ion exchange material, and means for initiating regeneration of the exchanger when the resistances between said pair of electrodes become substantially difierent from each other.

9. In combination with a main hydrogen ion exchanger, an auxiliary hydrogen ion exchanger, means for by-passing part of the eiiiuent from said main exchanger through said auxiliary ex- 7 changer, and means for measuring and comparing the electrical conductivities of the efliuents from the .two exchangers.

10. A process of operating a hydrogen ion exchanger in which a liquid is flowed through a bed of exchange material which comprises passing the liquid through a fixed quantity of the exchange material, measuring the conductivity of the liquid thus obtained, passing at least a portion of said treated liquid through an additional quantity of the exchange material, measuring the conductivity of the liquid after such additional treatment, and regenerating the bed when the conductivities thus measured become substantially difierent from each other.

11. A process of operating a hydrogen ion exchanger containing a bed of cation exchange material which comprises measuring the conductivity of the effluent from said exchanger, passing at least a portion of the effluent through a second bed of said :cation exchange material, and regenerating both of said beds when the two conductivities thus measured difier substantially from each other.

BERNARD ABEL SARD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,928,384 McCanna. Sept. 26,, 1933 2,209,487 Wagner July 30, 1940 FOREIGN PATENTS Number Country Date 569,660 Great Britain June 4, 1945 

1. A PROCEES OF DETERMINING WHEN TO REGENERATE A HYDROGEN ION EXCHANGER WHICH COMPRISES BYPASSING A PORTION OF THE EFFLUENT FROM THE EXCHANGER THROUGH A SMALL AUXILIARY HYDROEEN ION EXCHANGER, MEASURING THE CONDUCTIVITIES OF THE EFFLUENTS FROM SAID EXCHANGERS, AND REGENERATING SAID FIRST EXCHANGER WHEN SAID CONDUCTIVITIES BECOME SUBSTANTIALLY DIFFERENT FROM EACH OTHER. 